Sprint

Check your profiles mappings. Since the K2 is emulating a controller, you'd want to make sure that the normal method of sprinting is assigned to a key. Majority of game profiles will be pre-assigned to left shift. On the mappings, it is typically found under the left analog stick labeled "LC".

Note: If it is assigned to a key and it's still not working, make sure you don't have the same key assigned to another button as it can conflict in some games.